Plasma processing device member, plasma processing device comprising said plasma processing device member, and method for manufacturing plasma processing device member

ABSTRACT

A plasma processing device member according to the disclosure includes a base material and a film formed of an oxide, or fluoride, or oxyfluoride, or nitride of a rare-earth element, the film being disposed on at least part of the base material, the film including a surface to be exposed to plasma, the surface having an area occupancy of open pores of 8% by area or more, and an average diameter of open pores of 8 μm or less.

TECHNICAL FIELD

The present disclosure relates to a plasma processing device member, aplasma processing device including the plasma processing device member,and a method for manufacturing a plasma processing device member.

BACKGROUND ART

As one of members required to have high plasma resistance, use hasheretofore been made of a plasma processing device member including abase material and a film formed of an yttrium oxide, the film beingdisposed on the base material. In such a film, a low porosity (low areaoccupancy of open pores) of its surface to be exposed to plasma (whichmay also be hereinafter called merely “surface”) is required in theinterest of greater plasma resistance.

For example, Patent Literature 1 proposes a plasma processing containerinterior member which includes a ceramic base material, a Y₂O₃ sprayedcoating having a porosity of 5% or more on a surface of the ceramic basematerial by atmospheric plasma spraying, and a Y₂O₃ sprayed coatinghaving a porosity of less than 5% overlying the above-described sprayedcoating.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication JP-A2009-161848

SUMMARY OF INVENTION

A plasma processing device member according to the disclosure includes abase material and a film formed of an oxide, or fluoride, oroxyfluoride, or nitride of a rare-earth element, the film being disposedon at least part of the base material. The film includes a surface to beexposed to plasma, the surface have an area occupancy of open pores of8% by area or more, and an average diameter of open pores of 8 μm orless.

A plasma processing device according to the disclosure includes theplasma processing device member described above.

A method for manufacturing a plasma processing device member accordingto the disclosure includes: forming a first layer including an yttriumoxide as a main component on a base material by a sputtering method;applying smoothing processing to a film formation surface of the firstlayer; and forming a second layer including an yttrium oxide as a maincomponent on a smoothing-processed surface of the first layer by asputtering method.

BRIEF DESCRIPTION OF DRAWINGS

Other and further objects, features, and advantages of the inventionwill be more explicit from the following detailed description taken withreference to the drawings wherein:

FIG. 1A is a photograph of a surface to be exposed to plasma of a plasmaprocessing device member in accordance with one embodiment of thedisclosure taken by an optical microscope;

FIG. 1B is a sectional view schematically showing the plasma processingdevice member in accordance with one embodiment of the disclosure;

FIG. 1C is a sectional view schematically showing another example of theplasma processing device member in accordance with one embodiment of thedisclosure;

FIG. 2 is a schematic diagram of a sputtering apparatus used to obtainthe plasma processing device member in accordance with one embodiment ofthe disclosure;

FIG. 3A is a photograph of a surface to be exposed to plasma of a plasmaprocessing device member in accordance with another embodiment of thedisclosure taken by an optical microscope;

FIG. 3B is a side view showing the plasma processing device member inaccordance with another embodiment of the disclosure; and

FIG. 4 is a schematic diagram of a sputtering apparatus used to obtainthe plasma processing device member in accordance with anotherembodiment of the disclosure.

DESCRIPTION OF EMBODIMENTS

A plasma processing device member according to the disclosure will nowbe described in detail with reference to drawings.

FIG. 1A is a photograph of a surface to be exposed to plasma of theplasma processing device member according to the disclosure taken by anoptical microscope. FIG. 1B is a sectional view schematically showingthe plasma processing device member. FIG. 3C is a sectional viewschematically showing another example of the plasma processing devicemember.

A plasma processing device member 10 according to the disclosureincludes a base material 5 and a film 3 formed of a rare-earth elementoxide, the film 3 being disposed on at least part of the base material5. The surface to be exposed to plasma of the film 3 is provided with aplurality of open pores 4. FIGS. 1A to 1C show an example in which thesurface is provided with a plurality of open pores 4 a, 4 b, . . . , andshow an example in which an interior of the film 3 is provided with aplurality of closed pores 6.

Moreover, FIG. 1C shows the film 3 including a first layer (lower layer)1 located on the base material 5 and a second layer (upper layer) 2located on the first layer (lower layer) 1. For example, the ratiobetween a thickness t₁ of the first layer 1 and a thickness t₂ of thesecond layer 2, given as: t₁:t₂, stands at 4 to 6:6 to 4.

Examples of the base material 5 include quartz, aluminum with a purityof 99.999% (5N) or more, an aluminum alloy such as aluminum 6061 alloy,aluminum nitride ceramics, and aluminum oxide ceramics. The aluminumnitride ceramic refers to ceramics including an aluminum nitridecontent, i.e. the content of AlN-equivalent Al, of 90% by mass or morebased on 100% by mass of the constituents of the base material 5 in all.Moreover, the aluminum oxide ceramics refers to ceramics including analuminum oxide content, i.e. the content of Al₂O₃-equivalent Al, of 90%by mass or more based on 100% by mass of the constituents of the basematerial 5 in all. Note that the aluminum oxide ceramics may containmagnesium oxide, calcium oxide, silicon oxide, etc. in addition toaluminum oxide.

The film 3 is formed of a rare-earth element oxide. Examples of therare-earth element include yttrium (Y), cerium (Ce), samarium (Sm),gadolinium (Gd), dysprosium (Dy), erbium (Er), and ytterbium (Yb).Yttrium, in particular, is highly resistant to corrosion yet lessexpensive than other rare-earth elements. Thus, the use of yttrium asthe rare-earth element leads to a high degree of cost effectiveness.

The film 3 is not limited to those containing rare-earth element oxidesonly. Depending on the purity of a target used in a film 3-formingprocess, the device structure, etc., the film 3 may contain otherelements than the rare-earth element, such as fluorine (F), sodium (Na),magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S),chlorine (Cl), potassium (K), calcium (Ca), titanium (Ti), chromium(Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),zinc (Zn), and strontium (Sr).

The thickness of the film 3 is 10 μm or more and 200 μm or less, and themicro-Vickers hardness HmV of the film 3 is 7.5 GPa or more. Moreover,for example, given that the rare-earth element is yttrium, the film mayinclude, as a main component, an oxygen-deficient yttrium oxideexpressed as: Y₂O_(3-x) (0≤x<1). The yttrium oxide expressed by thecompositional formula given above exhibits semiconductivity, and it isthus possible to suppress surface charging of the film 3.

The constituents of the base material 5, as well as the constituents ofthe film 3, may be identified by X-ray diffractometer using CuKαradiation. For example, the content of each constituent may bedetermined by ICP (Inductively Coupled Plasma) optical emissionspectrometer or X-ray fluorescence analyzer.

The plasma processing device member according to the disclosure includesthe film 3 in which an area occupancy of the open pores 4 at the surfaceto be exposed to plasma is 8% by area or less, and an average diameterof the open pores 4 is 8 μm or less.

This structural design permits formation of fewer open pores 4 ofsmaller size at the surface to be exposed to plasma. Thus, the plasmaprocessing device member according to the disclosure has superior plasmaresistance. Moreover, since the number of particles generated fromwithin the open pores 4 is small and the size of generated particles issmall, it is possible to use the plasma processing device member for alonger period of time, and hence a plasma processing device providedwith the plasma processing device member according to the disclosure ishighly reliable.

A procedure for determining the average diameter and the area occupancyof the open pores 4 of the film 3 is as follows. The surface to beexposed to plasma is defined as a surface of measurement. DigitalMicroscope (VHX-5000 Series) manufactured by KEYENCE CORPORATION is setfor incident-light illumination technique of coaxial incidentillumination, illumination intensity of 255, and ZS20 lens, whichcorresponds to an objective lens, at 100-fold magnification. Then, darkspots (corresponding to the open pores) are extracted from an image of a7.223 mm² area (3.1 mm in transverse length and 2.33 mm in longitudinallength) of the surface of measurement obtained at a selected brightnesslevel in an automatic area measurement mode. After that, for example,with a threshold set to −20, the average diameter and the area occupancyof the open pores in the film 3 can be calculated. Note that the valueof the threshold may be adjusted according to the lightness of the darkspots.

The area occupancy of the open pores 4 at the surface to be exposed toplasma may be 4% by area or less, and the average diameter of the openpores 4 may be 4 μm or less.

Moreover, the film 3 may be configured so that a region in which theaverage diameter of the open pores 4 is 8 μm or less and the areaoccupancy of the open pores 4 from the surface of the film 3 is 8% byarea or less constitutes 5% or more of the entire thickness dimension ofthe film 3. Although the area occupancy of the open pores 4 basicallyapplies only to open pores at the surface to be exposed to plasma, forthe sake of calculation of area occupancy, pores that appear on thesurface during a surface grinding process are also defined as the openpores 4.

In the plasma processing device member 10 as exemplified in FIG. 1C, theabove described region corresponds to the second layer 2. That is, inthe case where the region in which the average diameter of the openpores 4 is 8 μm or less and the area occupancy of the open pores 4 is 8%by area or less is configured not only to exist in the surface but alsoto extend inwardly from the surface, even in a part of the film whichbecomes exposed as a fresh surface under exposure to plasma, the numberof particles generated from within the open pores 4 is small and thesize of generated particles is small. This makes it possible to carryout satisfactory plasma processing for a longer period of time. Thelower limit of the average diameter of the open pores 4, while notlimited to a particular value, is preferably greater than or equal to0.5 μm. Too small an open pore 4 size may impair the advantage of theinclusion of the open pores. Moreover, the lower limit of the areaoccupancy of the open pores 4, while not limited to a particular value,is preferably greater than or equal to 0.5%. Too small an open pore areaoccupancy may impair the advantage of the inclusion of the open pores.

Moreover, the film 3 may be provided with a cavity 8 which extends in athickness direction thereof from a recess 7 located at the film 3-facingsurface of the base material 5, and the cavity 8 may terminate withinthe film 3. As used herein the recess 7 refers to an open pore or cavitypresent at the film 3-facing surface of the base material 5, and alsorefers, prior to the formation of the film 3, to the surface of the basematerial 5.

When the film 3 is provided with the cavity 8, accumulation of residualstress can be restrained even under repeated rise and fall intemperature, and due to the cavity 8 lacking communication with theexterior thereof, it never occurs that particles within the cavity 8 goout of the film 3.

Moreover, a width at a part of the cavity 8 which is located close tothe surface of the film 3 may be smaller than a width at a part of thecavity 8 which is located close to the recess 7 of the base material 5,as viewed in a section taken along the thickness of the film 3. Withthis configuration, even if the tip of the cavity 8 opens on the surfaceof the film 3 due to a decrease in film thickness under exposure toplasma, particles within the cavity 8 is less likely to go out of thefilm 3, as contrasted to a configuration such that the width at the partof the cavity 8 which is located close to the surface of the film 3 islarger than the width at the part of the cavity 8 which is located closeto the recess 7 of the base material 5.

Moreover, the base material 5 formed of ceramics which includes aluminumoxide as a main component may contain at least one of yttrium aluminumgarnet (YAG), yttrium aluminum monoclinic (YAM), and yttrium aluminumperovskite (YAP) in the top of the film 3-facing covered surfacethereof.

This structural design permits enhanced chemical bonding of the film 3with the base material 5, and thus allows the film 3 to adhere morefirmly to the base material 5.

The following describes a method for manufacturing a plasma processingdevice member according to the disclosure.

A method for producing the base material will be described first.

Aluminum oxide (Al₂O₃) A powder having an average particle size of 0.4μm to 0.6 μm, and aluminum oxide B powder having an average particlesize of about 1.2 μm to 1.8 μm. Silicon oxide (SiO₂) powder as a Sisource, and calcium carbonate (CaCO₃) powder as a Ca source are alsoprepared. As the silicon oxide powder, fine powdery silicon oxide havingan average particle size of 0.5 μm or less is prepared. Moreover,magnesium hydroxide powder is used to obtain Mg-containing aluminaceramics. Note that other powdery materials than the aluminum oxide Apowder and the aluminum oxide B powder will be hereinafter collectivelycalled “first secondary component powder”.

A predetermined amount of each first secondary component powder isweighed out. After that, an aluminum oxide powder mixture is preparedfrom the aluminum oxide A powder and the aluminum oxide B powder in theamounts weighed out so that a mixture composed of the aluminum oxide Apowder and the aluminum oxide B powder in mass proportions ranging from40:60 to 60:40 can be obtained, and that the resulting alumina ceramicscontains Al, as an Al₂O₃-equivalent aluminum, in an amount of 99.4% bymass or more based on 100% by mass of the alumina ceramics constituentsin all. Moreover, for preparation of the first secondary componentpowder, preferably, on the basis of the measured amount of Na in thealuminum oxide powder mixture, certain amounts of the first secondarycomponent powder are weighed out so that the amount ratio between Na₂Oderived by conversion of the Na amount and the sum of the constituentsof the first secondary component powder (Si, Ca, etc. in thisexemplification) on an oxide basis stands at or below 1.1 in theresulting alumina ceramics.

Then, a slurry is prepared by mixing and stirring, in a stirrer, thealumina powder mixture and the first secondary component powder, withthe following components added: 1 to 1.5 parts by mass of a binder suchas PVA (polyvinyl alcohol); 100 parts by mass of a solvent; and 0.1 to0.55 parts by mass of a dispersant, based on 100 parts by mass of thealumina powder mixture and the first secondary component powder in all.

The slurry is spray-dried into granules, and the granules are shapedinto a molded body of predetermined shape by a powder press moldingapparatus, an isostatic pressing apparatus or the like. The molded bodyis subjected to cutting work on an as needed basis . Thus, a moldedproduct in substrate form is obtained.

Subsequently, the molded product is fired while being retained under thefollowing conditions: a firing temperature of 1500° C. or higher and1700° C. or lower; and the duration of retention time of four hours orlonger and six hours or shorter. After that, the molded product isground at a surface thereof where the film is to be formed by usingdiamond abrasive grains having an average particle size of 1 μm or moreand 5 μm or less, and a tin-made surface grinder. Thus, the basematerial 5 can be obtained.

Next, a method for forming the film will be described with reference toFIG. 2. FIG. 2 is a schematic diagram showing a sputtering apparatus 20,and the sputtering apparatus 20 includes: a chamber 15; a gas supplysource 13 connected in communication with the interior of the chamber15; an anode 14 and a cathode 12 which are disposed within the chamber15; and a target 11 connected to the cathode 12 side.

A procedure for forming the film is as follows. The base material 5obtained in the above-described manner is placed on the anode 14 sidewithin the chamber 15. Moreover, the target 11 including, as a maincomponent, a rare-earth element, or more specifically yttrium metal inthis example, is placed on the opposite side, i.e. on the cathode 12side, within the chamber 15. In this state, the interior of the chamber15 is brought under a reduced pressure by the operation of a vacuumpump, and, the gas supply source 13 supplies argon and oxygen as a gasG.

After that, a film of yttrium metal is formed on the surface of the basematerial 5 by sputtering in the presence of plasma P generated with theapplication of an electric field between the anode 14 and the cathode 12via a power supply. A film portion formed in one operation has athickness on the order of subnanometers. Subsequently, the yttrium metalfilm is subjected to an oxidizing process. A laminate having a totalfilm thickness of 10 μm or more and 200 μm or less is produced byalternately carrying out the yttrium metal film-forming process and theoxidizing process. Thus, the first layer 1 can be obtained.

In order to obtain the plasma processing device member containing atleast one of yttrium aluminum garnet (YAG), yttrium aluminum monoclinic(YAM), and yttrium aluminum perovskite (YAP) on a film-facing surface ofthe base material 5, the temperature of the base material 5 shouldpreferably be set at 400° C. or higher in the sputtering process. Any ofhigh-frequency power and DC power may be used as electric power which isprovided via the power supply.

After taking the base material 5 provided with the first layer 1 out ofthe chamber 15, smoothing processing is applied to a film formationsurface of the first layer 1. As used herein the smoothing processingrefers to, for example, a grinding process for grinding the filmformation surface of the first layer 1 into a treated surface (polishedsurface) with diamond abrasive grains having an average particle size of1 μm or more and 5 μm or less, and a tin-made surface grinder.

In order to obtain the plasma processing device member 10 including thecavity 8 which extends in the thickness direction from the recess 7located at the film-facing surface of the base material 5 and whichterminates within the film 3, the provision of the base material 5including the film-facing surface with open pores 4 having an averagediameter of 1 μm or more and 8 μm or less, and the process of grindingthe film formation surface of the first layer 1 until the averagediameter of open pores becomes 0.1 μm or more and 5 μm or less, shouldpreferably be carried out.

Moreover, when a film on the base material 5 including the film-facingsurface with open pores having an average diameter of 1 μm or more and 8μm or less is formed by means of the sputtering apparatus 20 as shown inFIG. 2, the width at the part of the cavity 8 which is located close tothe surface of the film is smaller than the width at the part of thecavity 8 which is located close to the recess 7 of the base material 5,as viewed in the section taken along the thickness of the film 3.Moreover, when the film formation surface of the first layer 1 is grounduntil the average diameter of open pores becomes 0.1 μm or more and 5 μmor less, and the second layer 2 is formed as will hereafter bedescribed, the cavity 8 is closed within the film 3.

The second layer 2 including an yttrium oxide as a main component isformed on the treated surface of the first layer 1 in the same manner asthat for forming the first layer 1. Thus, the plasma processing devicemember 10 according to the disclosure can be obtained.

The plasma processing device member 10 according to the disclosureobtained by the above-described manufacturing method can achieve thereduced number of particles generated from within the open pores and thesmall size of generated particles, and is thus applicable to, forexample, a radio-frequency transmissive window member that allowsradio-frequency radiation for plasma generation to pass therethrough, ashower plate for distribution of gas for plasma production, and asusceptor for holding semiconductor wafers.

A plasma processing device member in accordance with another embodimentof the disclosure will now be described in detail with reference todrawings.

As shown in FIG. 3B, a plasma processing device member 21 according tothe disclosure includes a base material 22 and a film 23 formed of arare-earth element oxide, or a rare-earth element fluoride, or arare-earth element oxyfluoride, or a rare-earth element nitride, thefilm 23 being disposed on at least part of the base material 22. FIG. 3Bshows an example in which one upper surface 22 a of the base material 22is covered with the film 23.

A surface to be exposed to plasma of the film 23 (upper surface asviewed in FIG. 3B, which may also be hereinafter called merely“surface”), has an arithmetic mean roughness Ra of 0.01 μm or more and0.1 μm or less. In addition, the surface is provided with a plurality ofpores 24. FIG. 3A shows the surface provided with a plurality of pores24 a, 24 b, . . . . The surface to be exposed to plasma of the film 23is construed as encompassing a part of the film 23 which becomes exposedas a fresh surface due to a decrease in film thickness under exposure toplasma.

The arithmetic mean surface roughness Ra may be determined inconformance with JIS B 0601-2013. More specifically, the Ra measurementis carried out with use of Surface Roughness Measuring InstrumentSURFCORDER (Model SE500) manufactured by Kosaka Laboratory Ltd. underthe following conditions: a stylus tip radius of 5 μm; a measurementlength of 2.5 mm; and a cutoff value of 0.8 mm.

A clear illustration of the film 23 in FIG. 3B is just for the sake ofclarity about the presence of the film 23, and hence the correlation inthickness between the base material 22 and the film 23 is not faithfullyrepresented in FIG. 3B.

The film 23 is formed of a rare-earth element oxide, or a rare-earthelement fluoride, or a rare-earth element oxyfluoride, or a rare-earthelement nitride (oxides, fluorides, oxyfluorides, and nitrides will behereinafter collectively called “compounds”). Examples of the rare-earthelement include yttrium (Y), cerium (Ce), samarium (Sm), gadolinium(Gd), dysprosium (Dy), erbium (Er), and ytterbium (Yb). Yttrium, inparticular, is highly resistant to corrosion yet less expensive thanother rare-earth elements. Thus, the use of yttrium as the rare-earthelement allows a high degree of cost effectiveness to be achieved.

Examples of compositional formulae for yttrium compounds include Y₂O₃,(0≤x≤1), YF₃, YOF, Y₅O₄F₇, Y₅O₆F₇, Y₆O₅F₈, Y₇O₆F₉, Y₁₇O₁₄F₂₃, and YN.

The film 23 is not limited to those containing rare-earth elementcompounds only. Depending on the purity of a target used in a film23-forming process, the device structure, etc., the film 23 may containother elements than the rare-earth element, such as fluorine (F), sodium(Na), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P),sulfur (S), chlorine (Cl), potassium (K), calcium (Ca), titanium (Ti),chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),copper (Cu), zinc (Zn), and strontium (Sr). The constituents of the film23 may be identified by using X-ray diffractometer for thin films.

Examples of the base material 22 include quartz, aluminum with a purityof 99.999% (5N) or more, an aluminum alloy such as aluminum 6061 alloy,aluminum nitride ceramics, and aluminum oxide ceramics. As to thealuminum nitride ceramics and the aluminum oxide ceramics, for example,the aluminum oxide ceramics refers to ceramics including an aluminumoxide content, i.e. the content of Al₂O₃-equivalent Al, of 90% by massor more based on 100% by mass of the constituents of the base material22 in all. Note that the aluminum oxide ceramics may contain magnesiumoxide, calcium oxide, silicon oxide, etc. in addition to aluminum oxide.

The film 23 is provided with a plurality of pores, and a value Aobtained by subtracting an average equivalent circle diameter of thepores from an average distance between centroids of adjacent pores is 28μm or more and 48 μm or less.

The value A falling in the range of 28 μm or more to 48 μm or lessindicates that the number of pores is small, the pore size is small, andthe pores are dispersed. That is, in the plasma processing device member21 that fulfills the aforestated design conditions, fewer particles aregenerated from within the pores. Moreover, even if a microcrackoriginates in a certain pore, nearby pores sufficiently dispersed as toblock the propagation of the microcrack help reduce the number ofparticles resulting from microcrack propagation.

Moreover, in the plasma processing device member 21 according to thedisclosure, the area occupancy of the plurality of pores in the film 23may be 1.5% by area or more and 6% by area or less. With the areaoccupancy of the pores falling in the range of 1.5% by area or more and6% by area or less, even if a microcrack appears at the surface to beexposed to plasma (including a part of the film which becomes exposed asa fresh surface due to a decrease in film thickness under exposure toplasma), the pores serve to block the propagation of the microcrack,with the consequent reduced number of microcrack-caused particles.Moreover, the low area occupancy of the pores present in the surface tobe exposed to plasma is conducive to further reduction in the number ofparticles generated from within the pores.

Moreover, in the plasma processing device member 21 according to thedisclosure, an average pore spheroidization rate in the film 23 may be60% or more. With the pore spheroidization rate falling in this range,residual stress is less likely to accumulate around the pores, with theconsequent reduction of generation of particles from around the poresunder exposure to plasma.

As used herein the pore spheroidization rate is a conversion of a ratedefined by the graphite area method, and is defined by the followingmathematical expression (1):

pore spheroidization rate (%)=(pore actual area)/(area of minimumcircumscribed circle of pore)×100   (1).

The average pore spheroidization rate is preferably 62% or more.

Moreover, the average distance between the centroids of the pores, theaverage equivalent circle diameter of the pores, the area occupancy ofthe pores, and the pore spheroidization rate are determined in thefollowing manner.

First, the surface of the film under a digital microscope at 100-foldmagnification is observed, and an image of a 7.68 mm² area of thesurface under observation (3.2 mm in transverse length and 2.4 mm inlongitudinal length) is taken by a CCD camera. The image is subjected toimage analysis using Image Analysis Software “AZO-KUN (Ver 2.52)”(trademark) manufactured by Asahi Kasei Engineering Corporation (in whatfollows, the term “Image Analysis Software “AZO-KUN”” refers to theimage analysis software manufactured by Asahi Kasei EngineeringCorporation throughout the description) to measure the average distancebetween the centroids of the pores by means known as the inter-centroiddistance method for dispersivity measurement.

Moreover, the average equivalent circle diameter of the pores, the areaoccupancy of the pores, and the pore spheroidization rate may bedetermined through the analysis of the same image as the describedobserved image by means known as the particle analytical method usingImage Analysis Software “AZO-KUN”. A part of the observed image whichcorresponds to the pore appears to be a dark spot which is easilydiscernible.

For example, measurements using the inter-centroid distance method andthe particle analytical method are carried out under the followingconditions: a threshold, used as a measure of image brightness, of 140;an image lightness of low level; an area for small-figure removal of 1μm²; and application of a denoising filter. While the threshold set forthe described measurements is 140, the value of the threshold may beadjusted according to the brightness of the observed image. That is,after setting the lightness at a low level, selecting a manual imagebinarization mode, setting the area for small-figure removal at 1 μm²,and applying a denoising filter, threshold adjustment is carried out sothat the shape of a marker whose size varies according to the value ofthe threshold can coincide with pore shape in the observed image.

Moreover, in the plasma processing device member 21 according to thedisclosure, a kurtosis Ku1 of equivalent circle diameters of theplurality of pores in the film 23 may be 0.5 or more and 2 or less. Withthe kurtosis Ku1 of the equivalent circle diameters of the pores fallingin this range, the equivalent circle diameters of the pores are narrowlydistributed, and also the number of pores having extraordinarily largeequivalent circle diameters is small. This produces the effect ofretarding microcrack propagation, reduces the number of particlesgenerated from within the pores, and provides superior plasmaresistance. Moreover, in a grinding process subsequent to filmformation, the film 23 made to fulfill the aforestated design conditionsmay be given desired surface properties in a minimum grinding amount onthe strength of its imperviousness to partial wear. The kurtosis Ku1 ispreferably 1.3 or more and 1.9 or less.

As used herein the kurtosis Ku1 refers to an index (statistic)indicating how much a peak and tails of the distribution differ in thenormal distribution. When the kurtosis Ku1>0, the distribution becomes aleptokurtic distribution having a sharp-pointed peak and longer andheavier tails. When the kurtosis Ku1=0, the distribution becomes thenormal distribution. When the kurtosis Ku1<0, the distribution becomes aplatykurtic distribution having a rounded peak and shorter and thinnertails. The kurtosis Ku1 of the equivalent circle diameters of the poresmay be obtained by measurement using the function Kurt provided in Excel(registered trademark) manufactured by Microsoft Corporation.

Moreover, in the plasma processing device member 21 according to thedisclosure, a skewness Sk1 of the equivalent circle diameters of theplurality of pores in the film 23 may be 3 or more and 5.6 or less. Withthe skewness Sk1 of the equivalent circle diameters of the pores fallingin this range, the value of the average equivalent circle diameter ofthe pores is small, and the number of pores having extraordinarily largeequivalent circle diameters is also small. This produces the effect ofretarding microcrack propagation, reduces the number of particlesgenerated from within the pores, and provides superior plasmaresistance. Moreover, in a grinding process subsequent to filmformation, the film 23 made to fulfill the aforestated design conditionsmay be given desired surface properties in a minimum grinding amount onthe strength of its imperviousness to partial wear. The skewness Sk1 ispreferably 3.2 or more and 5.3 or less.

As used herein the skewness Sk1 refers to an index (statistic)indicating how much the distribution is distorted from the normaldistribution, in other words, an index indicating the bilateral symmetryof the distribution. When the skewness Sk1>0, the distribution becomes askewed distribution with its tail shifted rightward. When the skewnessSk1=0, the distribution becomes a bilaterally symmetric distribution.When the skewness Sk1<0, the distribution becomes a skewed distributionwith its tail shifted leftward. The skewness Sk1 of the equivalentcircle diameters of the pores may be obtained by measurement using thefunction SKEW provided in Excel (registered trademark) manufactured byMicrosoft Corporation.

Moreover, in the plasma processing device member 21 according to thedisclosure, a kurtosis Ku2 of distances between centroids of the poresin the film 23 may be 0.1 or more and 0.5 or less. With the kurtosis Ku2of the distances between the centroids of the pores falling in thisrange, the distances between the centroids are narrowly distributed, andalso extraordinarily long distances between the centroids are small.This provides the effect of retarding microcrack propagation, and alsoreduces uneven distribution of residual stress.

Moreover, in the plasma processing device member 21 according to thedisclosure, a skewness Sk2 of the distances between centroids of thepores in the film 23 may be 0.5 or more and 1 or less.

Moreover, a relative density of the film 23 may be 98% or more, or inparticular may be 99% or more . The film 23 having the relative densityfalling in this range is a dense film which suffers little particlegeneration even when undergoing thickness reduction under exposure toplasma. In determining the relative density of the film 23, an actuallymeasured film density is first obtained by X-ray Reflectometry (XRR)using X-ray diffractometer for thin films, and the ratio of the actuallymeasured density to a theoretical density is then derived.

As described earlier, the area occupancy of the pores is preferably 1.5%by area or more and 6% by area or less. Meanwhile, the relative densityof the film 23 is preferably 98% or more. There seems to be nocorrelation between the area occupancy of the pores and the relativedensity of the film 23. This is because the area occupancy of the poresis determined through image analysis, whereas the film relative densityis determined by XRR. XRR allows X-rays to pass through the film 23 formeasurement. In some cases, a part of the film 23 where a pore-bearingpart and a pore-free part are overlapped in the direction of X-raytransmission is judged as a “pore-free region”. On this account slightlyhigher-than-normal levels of the relative density of the film 23 may bedetected in XRR measurement.

Thus, the plasma processing device member 21 according to the disclosureis less prone to particle generation, and a plasma processing deviceprovided with the plasma processing device member 21 is highly reliablecorrespondingly.

The following describes a method of manufacturing a plasma processingdevice member according to the disclosure.

A method for producing the base material will be described first.

Aluminum oxide (Al₂O₃) A powder having an average particle size of 0.4μm to 0.6 μm, and aluminum oxide B powder having an average particlesize of about 1.2 μm to 1.8 μm are prepared. Silicon oxide (SiO₂) powderas a Si source, and calcium carbonate (CaCO₃) powder as a Ca source arealso prepared. As the silicon oxide powder, fine powdery silicon oxidehaving an average particle size of 0.5 μm or less is prepared. Moreover,magnesium hydroxide powder is used to obtain Mg-containing aluminaceramics. Note that other powdery materials than the aluminum oxide Apowder and the aluminum oxide B powder will be hereinafter collectivelycalled “first secondary component powder”.

A predetermined amount of each first secondary component powder isweighed out. After that, an aluminum oxide powder mixture is preparedfrom the aluminum oxide A powder and the aluminum oxide B powder in theamounts weighed out so that a mixture composed of the aluminum oxide Apowder and the aluminum oxide B powder in mass proportions ranging from40:60 to 60:40 can be obtained, and that the resulting alumina ceramicscontains Al, as an Al₂O₃-equivalent aluminum, in an amount of 99.4% bymass or more based on 100% by mass of the alumina ceramics constituentsin all. Moreover, for preparation of the first secondary componentpowder, preferably, on the basis of the measured amount of Na in thealuminum oxide powder mixture, certain amounts of the first secondarycomponent powder are weighed out so that the amount ratio between Na₂Oderived by conversion of the Na amount and the sum of the constituentsof the first secondary component powder (Si, Ca, etc. in thisexemplification) on an oxide basis stands at or below 1.1 in theresulting alumina ceramics.

Then, a slurry is prepared by mixing and stirring, in a stirrer, thealumina powder mixture and the first secondary component powder, withthe following components added: 1 to 1.5 parts by mass of a binder suchas PVA (polyvinyl alcohol); 100 parts by mass of a solvent; and 0.1 to0.55 parts by mass of a dispersant, based on 100 parts by mass of thealumina powder mixture and the first secondary component powder in all.

The slurry is spray-dried into granules, and the granules are shapedinto a molded body of desired shape by a powder press molding apparatus,an isostatic pressing apparatus or the like. The molded body issubjected to cutting work on an as needed basis . Thus, a molded productin substrate form is obtained.

Subsequently, the molded product is fired while being retained under thefollowing conditions: a firing temperature of 1500° C. or higher and1700° C. or lower; and the duration of retention time of four hours orlonger and six hours or shorter. After that, the molded product isground at a surface thereof where the film 23 is to be formed by usingdiamond abrasive grains having an average particle size of 1 μm or moreand 5 μm or less, and a tin-made surface grinder. Thus, the basematerial 25 can be obtained.

Next, a method for forming the film will be described with reference toFIG. 4. FIG. 4 is a schematic diagram showing a sputtering apparatus 40,and the sputtering apparatus 40 includes: a chamber 35; a gas supplysource 33 connected in communication with the interior of the chamber35; an anode 34 and a cathode 32 which are disposed within the chamber35; and a target 31 connected to the cathode 32 side.

A procedure for forming the film is as follows. The base material 25obtained in the above-described manner is placed on the anode 34 sidewithin the chamber 35. Moreover, the target 31 including, as a maincomponent, a rare-earth element, or more specifically yttrium metal inthis example, is placed on the opposite side, i.e. on the cathode 32side, within the chamber 35. In this state, the interior of the chamber35 is brought under a reduced pressure by the operation of a vacuumpump, and, the gas supply source 33 supplies argon and oxygen as a gasG.

After that, a film of yttrium metal is formed on the surface of the basematerial 25 by sputtering in the presence of plasma P generated with theapplication of an electric field between the anode 34 and the cathode 32via a power supply. A film portion formed in one operation has athickness on the order of subnanometers. Subsequently, the yttrium metalfilm is subjected to an oxidizing process. A laminate having a totalfilm thickness of 10 μm or more and 200 μm or less is produced byalternately carrying out the yttrium metal film-forming process and theoxidizing process. Thus, the plasma processing device member includingthe resulting film of the yttrium oxide according to the disclosure isobtained.

In order to obtain the plasma processing device member in which the areaoccupancy of the plurality of pores is 1.5% by area or more and 6% byarea or less, the area occupancy of pores at the film-facing surface ofthe base material should preferably be 1% by area or more and 5% by areaor less.

Moreover, in order to obtain the plasma processing device member inwhich the average spheroidization rate of the plurality of pores is 60%or more, the average spheroidization rate of the pores at thefilm-facing surface of the base material should preferably be 62% ormore.

Moreover, in order to obtain the plasma processing device member inwhich the kurtosis Ku of the equivalent circle diameters of theplurality of pores is 0.5 or more and 2 or less, the kurtosis Ku of theequivalent circle diameters of the pores at the film-facing surface ofthe base material should preferably be 0.6 or more and 1.8 or less.

Moreover, in order to obtain the plasma processing device member inwhich the skewness Sk of the equivalent circle diameters of theplurality of pores is 3 or less and 5.6 or less, the skewness Sk of theequivalent circle diameters of the pores at the film-facing surface ofthe base material should preferably be 3.1 or less and 5.4 or less.

Moreover, in order to form a film of yttrium fluoride, the yttrium metalfilm should preferably be subjected to a fluoridizing process instead ofthe oxidizing process.

Moreover, in order to form a film of yttrium oxyfluoride, a laminateshould preferably be obtained by alternately carrying out the yttriummetal film-forming process, the oxidizing process and the fluoridizingprocess in the order named.

Moreover, in order to form a film of yttrium nitride, the yttrium metalfilm should preferably be subjected to a nitriding process instead ofthe oxidizing process.

Any of high-frequency power and DC power may be used as electric powerwhich is provided via the power supply.

The plasma processing device member according to the disclosure obtainedby the above-described manufacturing method achieves reduction of bothof the number of particles generated from within the pores and thenumber of particles resulting from microcrack propagation, and is thusapplicable to, for example, a radio-frequency transmissive window memberthat allows radio-frequency radiation for plasma generation to passtherethrough, a shower plate for distribution of gas for plasmaproduction, and a susceptor for holding semiconductor wafers.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and the rangeof equivalency of the claims are therefore intended to be embracedtherein. For example, inventive combinations of the embodimentsaccording to the disclosure are also considered as coming within thescope of the invention.

REFERENCE SIGNS LIST

1: First layer (lower layer)

2: Second layer (upper layer)

3: Film

4: Open pores

5: Base material

6: Closed pores

7: Recess

8: Cavity

10: Plasma processing device member

11: Target

12: Cathode

13: Gas supply source

14: Anode

15: Chamber

20: Sputtering apparatus

1. A plasma processing device member, comprising: a base material; and afilm formed of an oxide, or fluoride, or oxyfluoride, or nitride of arare-earth element, the film being disposed on at least part of the basematerial, the film comprising a surface to be exposed to plasma, thesurface having an area occupancy of open pores of 8% by area or less,and an average diameter of open pores of 8 μm or less.
 2. The plasmaprocessing device member according to claim 1, wherein the film isconfigured so that a region of the film in which the average diameter ofopen pores is 8 μm or less and the area occupancy of open pores from thesurface of the film is 8% by area or less constitutes 5% or more of anentire thickness dimension of the film.
 3. The plasma processing devicemember according to claim 1, wherein the film is provided with a cavitywhich extends in a thickness direction of the film from a recess locatedat a surface of the base material which faces the film, and the cavityterminates within the film.
 4. The plasma processing device memberaccording to claim 3, wherein a width at a part of the cavity which islocated close to the surface of the film is smaller than a width at apart of the cavity which is located close to the recess of the basematerial, as viewed in a section taken along a thickness of the film. 5.The plasma processing device member according to claim 1, wherein therare-earth element comprises yttrium.
 6. The plasma processing devicemember according to claim 5, wherein the base material is formed ofceramics comprising aluminum oxide as a main component, and comprises,in a top of a surface of the base material which surface faces the film,at least one of yttrium aluminum garnet (YAG), yttrium aluminummonoclinic (YAM), and yttrium aluminum perovskite (YAP).
 7. A plasmaprocessing device, comprising: the plasma processing device memberaccording to claim
 1. 8. A method of manufacturing a plasma processingdevice member, comprising: forming a first layer comprising an yttriumoxide as a main component on a base material by a sputtering method;applying smoothing processing to a film formation surface of the firstlayer; and forming a second layer comprising an yttrium oxide as a maincomponent on a smoothing-processed surface of the first layer by asputtering method.